Mechanisms of high durability performance of plain and blended cements

Arabic Abstract

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English Abstract

In this research, an attempt has been made to study the mechanisms controlling the performance of plain and blended cements against corrosion of reinforcement and ASR. The effect of various compositional and environmental factors, such as C₃A and alkali contents, concomitant presence of sulfates, temperature and mode of occurrence of chlorides, on chloride binding and pore solution alkalinity has been studied in plain cements, in an effort to evaluate their influence on mechanism of corrosion resistance. Mechanisms controling resistance to corrosion and ASR of blended cements, formulated using fly ash, blast furnace slag and microsilica have been studied through their effect on chemical environment and physical characteristics of hardened concrete. Results show that high C₃A cements have more chloride binding capacity than low C₃A cements, explaining their higher corrosion resistance. Increase in curing temperature and alkali content of cement and concomitant presence of sulfates decrease chloride binding capacity in plain cements. Plain cement binds more primary chlorides than secondary external chlorides. Fly ash and slag have little effect on chemical environment of concrete compared to microsilica, which drastically increases aggressivity of the chemical environment. The blending materials bring about significant improvement in the physical structure of concrete through pore refinement, decrease in permeability, chloride and oxygen diffusion and increase in electrical resistivity. These significant improvements in the physical characteristics due to blending materials are responsible for the improved corrosion resistance of the blended cements. Also, the blending materials significantly reduce OH concentration in pore solution. The reduction in the OH concentration and possibly the improved physical structure of blended cements are responsible for their incresed resistance against ASR.